“Specifications of the Radio Data System for VHF/FM Broadcasting,” European Broadcasting Union, Brussels, March, 1984, describes a standard for transmitting supplemental information, in addition to radio program content, over a radio frequency. The supplemental information includes a program identifier, PI (Program Identification), for the unambiguous identification of a program content that is transmitted equally over one or a plurality of radio frequencies, a traffic radio identifier, TP (Traffic Program), that designates a program broadcasting traffic messages, a list of alternative frequencies, AF (Alternative Frequencies), over which the same program is transmitted as it is over a currently receiving radio frequency, and information regarding other program networks, ON (Other Networks). This supplemental information, in addition to other functions, makes possible an automatic tuning of the radio receiver to a radio frequency. The supplemental information is transmitted in so-called groups, in accordance with information to be transmitted of different types, having in each case four blocks each having 26 bits, of which 16 bits contain the actual information and the other 10 bits function for detecting and correcting errors as well as for synchronizing the receiver to the RDS signal.
In groups of the “3A” and “3B” type, or, in accordance with the standard DIN EN 50 067 based on the EBU specification—“Specification of the Radio Data System (RDS),” German version EN 50 067, 1992, German Electro-Technical Commission in DIN and VDE (DKE), Beuth Press GmbH, Berlin—, in groups of the “14A” and “14B” type, information about other networks, i.e., references to other radio station offerings, is transmitted. This information about ON (other networks), or, in the language of DIN EN 50 067, expanded information about other networks, EON (Enhanced Other Networks), includes information about the transmitting frequencies over which these other station offerings are transmitted and also includes the TP and TA information of each station's programming to which reference is made.
In car radios, for example, in devices of the Blaupunkt Works GmbH, Hildesheim, this information is used for the purpose of bringing traffic information to the user's attention even while he is listening to radio programming over which no traffic information is transmitted. For this purpose, the aforementioned apparatuses evaluate the EON information such that in the event of traffic information marked by the TA identifier is within the programming to which the EON information refers, the receiver, for the duration of the traffic information, is reset from the frequency being instantaneously received to this one, and therefore the reproduction of the traffic information is assured. After the termination of the traffic information, the receiver is once again tuned to the original radio frequency, that is not transmitting any traffic information.
In German Patent No. 43 06 595, a radio receiver is described in the form of a car radio, which has the capability of automatically recording traffic information that is designated as such by an identifier and that is transmitted over a radio frequency. The radio receiver described also possesses a monitoring operating state, in which, on the one hand, it is possible to continue recording current traffic information even after being switched off, while, on the other hand, avoiding an excessive stressing of the vehicle battery, which functions as the energy source for the radio receiver. During the monitoring state, the means necessary for receiving and evaluating a radio frequency are supplied with power in a clocked fashion, the power nevertheless completely switching off the assemblies that have especially high energy consumption, such as an NF (Low Frequency) output stage. During the monitoring state, the receiver, while the receiving evaluating means are switched on, is tuned to a preestablished radio frequency, and the received radio frequency monitors for the presence of an identifier designating traffic information. In the event an identifier is detected, the receiving, evaluating, and subsequently recording means are supplied with power for the duration of the identifier, and the information is recorded.
The radio receiver described in German Patent No. 43 06 595 assumes that, before switching the device to the monitoring state, the receiving element is set at a radio frequency over which traffic information is transmitted. If this is not the case, then in conventional car radios, for example, in the aforementioned devices of the Blaupunkt Works GmbH, Hildesheim, a TP-oriented transmitter search is initiated, i.e., a search for radio frequencies that broadcast traffic information. In the event that a plurality of TP radio frequencies is detected, the one having the clearest reception is set as the receiving frequency. The result is that, under certain circumstances, when the radio receiver is started up, transmitters that are not known to the user are stored in the traffic information storage unit, which can confuse the user. In addition, it is possible that traffic information is stored that is from a distant radio transmitter and that is irrelevant to the current location of the receiver, which adds to the confusion and also limits the storage space, usually in short supply, to the detriment of relevant traffic information.